Quick And Very Dirty Repair Gets Smoked PLC Back In The Game

November 21, 2024 by Dan Maloney 11 Comments

When electronics release the Magic Smoke, more often than not it’s a fairly sedate event. Something overheats, the packaging gets hot enough to emit that characteristic and unmistakable odor, and wisps of smoke begin to waft up from the defunct component. Then again, sometimes the Magic Smoke is more like the Magic Plasma, as was the case in this absolutely smoked Omron programmable logic controller.

Normally, one tasked with repairing such a thing would just write the unit off and order a replacement. But [Defpom] needed to get the pump controlled by this PLC back online immediately, leading to the somewhat unorthodox repair in the video below. Whatever happened to this poor device happened rapidly and energetically, taking out two of the four relay-controlled outputs. [Defpom]’s initial inspection revealed that the screw terminals for one of the relays no longer existed, one relay enclosure was melted open, its neighbor was partially melted, and a large chunk of the PCB was missing. Cleaning up the damaged relays revealed what the “FR” in “FR4” stands for, as the fiberglass weave of the board was visible after the epoxy partly burned away before self-extinguishing.

With the damaged components removed and the dangerously conductive carbonized sections cut away, [Defpom] looked for ways to make a temporary repair. The PLC’s program was locked, making it impossible to reprogram it to use the unaffected outputs. Instead, he redirected the driver transistor for the missing relay two to the previously unused and still intact relay one, while adding an outboard DIN-mount relay to replace relay three. In theory, that should allow the system to work with its existing program and get the system back online.

Did it work? Sadly, we don’t know, as the video stops before we see the results. But we can’t see a reason for it not to work, at least temporarily while a new PLC is ordered. Of course, the other solution here could have been to replace the PLC with an Arduino, but this seems like the path of least resistance. Which, come to think of it, is probably what caused the damage in the first place.

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Automating 3D Printer Support Hardware

June 6, 2024 by Bryan Cockfield 22 Comments

While 3D printers have evolved over the past two decades from novelties to powerful prototyping tools, the amount of support systems have advanced tremendously as well. From rudimentary software that required extensive manual input and offered limited design capabilities, there’s now user-friendly interfaces with more features than you could shake a stick at. Hardware support has become refined as well with plenty of options including lighting, ventilation, filament recycling, and tool changers. It’s possible to automate some of these subsystems as well like [Caelestis Workshop] has done with this relay control box.

This build specifically focuses on automating or remotely controlling the power, enclosure lighting, and the ventilation system of [Caelestis Workshop]’s 3D printer but was specifically designed to be scalable and support adding other features quickly. A large power supply is housed inside of a 3D printed enclosure along with a Raspberry Pi. The Pi controls four relays which are used to control these various pieces hardware along with the 3D printer. That’s not the only thing the Pi is responsible for, though. It’s also configured to run Octoprint, a piece of open-source software that adds web interfaces for 3D printers and allows their operation to be monitored and controlled remotely too.

With this setup properly configured, [Caelestis Workshop] can access their printer from essentially any PC, monitor their prints, and ensure that ventilation is running. Streamlining the print process is key to reducing the frustration of any 3D printer setup, and this build will go a long way to achieving a more stress-free environment. In case you missed it, we recently hosed a FLOSS Weekly episode talking about Octoprint itself which is worth a listen especially if you haven’t tried this piece of software out yet.

Reinventing Rotary Switches With Stepper Motors

May 27, 2024 by Al Williams 22 Comments

When you need to make very tiny measurements, even noise in closed relays can throw you off. [Marco] was able to observe this effect and wanted to build a switch that didn’t have this problem. He found a technical paper that used rotary switches operated by stepper motors instead of relays. So he decided to try making his own version. The video below shows how it turned out.

The first part of the video talks about why relays sometimes inject a tiny voltage into a closed circuit. He then looks at costly switches that would work. However, since he needed many switches, he decided to roll his own.

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A Smart Power Distribution Unit For Home Automation

April 25, 2024 by Bryan Cockfield 28 Comments

Power distribution units, as the name implies, are indispensable tools to have available in a server rack. They can handle a huge amount of power for demands of intensive computing and do it in a way that the wiring is managed fairly well. Plenty of off-the-shelf solutions have remote control or automation capabilities as well, but finding none that fit [fmarzocca]’s needs or price range, he ended up building his own essentially from scratch that powers his home automation system.

Because it is the power supply for a home automation system, each of the twelve outlets in this unit needed to be individually controllable. For that, three four-channel relay boards were used, each driven by an output on an ESP32. The ESP32 is running the Tasmota firmware to keep from having to reinvent the wheel, while MQTT was chosen as a protocol for controlling these outlets to allow for easy integration with the existing Node-RED-based home automation system. Not only is control built in to each channel, but the system can monitor the power consumption of each outlet individually as well. The entire system is housed in a custom-built sheet metal enclosure and painted to blend in well with any server rack.

Adding a system like this to a home automation system can simplify a lot of the design, and the scalable nature means that a system like this could easily be made much smaller or much larger without much additional effort. If you’d prefer to keep your hands away from mains voltage, though, we’ve seen similar builds based on USB power instead, with this one able to push around 2 kW.

Crank-Powered Train Uses No Batteries Or Plugs

April 12, 2024 by Kristina Panos 5 Comments

The prolific [Peter Waldraff] is at back it with another gorgeous micro train layout. This time, there are no plugs and no batteries. And although it’s crank-powered, it can run on its own with the flip of a switch. How? With a supercapacitor, of course.

The crank handle is connected a 50 RPM motor that acts as a generator, producing the voltage necessary to both power the train and charge up the supercapacitor. As you’ll see in the video below, [Peter] only has to move the train back and forth about two or three times before he’s able to flip the switch and watch it run between the gem mine and the cliff by itself.

The supercapacitor also lights up the gem mine to show off the toiling dwarfs, and there’s a couple of reed switches at either end of the track and a relay that handles the auto-reverse capability. Be sure to stick around to the second half of the video where [Peter] shows how he built this entire thing — the box, the layout, and the circuit.

Want to see more of [Peter]’s trains and other work? Here you go.

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A Long-Range Meshtastic Relay

April 3, 2024 by Bryan Cockfield 22 Comments

In the past few years we’ve seen the rise of low-power mesh networking devices for everything from IoT devices, weather stations, and even off-grid communications networks. These radio modules are largely exempt from licensing requirements due to their low power and typically only operate within a very small area. But by borrowing some ideas from the licensed side of amateur radio, [Peter Fairlie] built this Meshtastic repeater which can greatly extend the range of his low-power system.

[Peter] is calling this a “long lines relay” after old AT&T microwave technology, but it is essentially two Heltec modules set up to operate as Meshtastic nodes, where one can operate as a receiver while the other re-transmits the received signal. Each is connected to a log-periodic antenna to greatly increase the range of the repeater along the direction of the antenna. These antennas are highly directional, but they allow [Peter] to connect to Meshtastic networks in the semi-distant city of Toronto which he otherwise wouldn’t be able to hear.

With the two modules connected to the antennas and enclosed in a weatherproof box, the system was mounted on a radio tower allowing a greatly increased range for these low-power devices. If you’re familiar with LoRa but not Meshtastic, it’s become somewhat popular lately for being a straightforward tool for setting up low-power networks for various tasks. [Jonathan Bennett] explored it in much more detail as an emergency communications mode after a tornado hit his home town.

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Multiply Your Multimeter With Relays And USB

April 2, 2024 by Dan Maloney 10 Comments

Multimeters are a bit like potato chips: you can’t have just one. But they’re a lot more expensive than potato chips, especially the good ones, and while it’s tempting to just go get another one when you need to make multiple measurements, sometimes it’s not practical. That’s why something like this 2×4 relay-based multiplexer might be a handy addition to your bench

In this age of electronics plenty, you’d think that a simple USB relay board would be easy enough to lay hands on. But [Petteri Aimonen] had enough trouble finding a decent one that it became easier to just roll one up from scratch. His goal was to switch both the positive and negative test leads from up to four instruments to a common set of outputs, and to have two independent switching banks, for those times when four-lead measurements are needed. The choice of relay was important; [Petteri] settled on a Panasonic DPDT signal relay with low wetting current contacts and a low-current coil. The coils are driven by a TBD62783A 8-channel driver chip, while an STM32 takes care of USB duties.

The mechanical design of this multiplexer is just as slick as the electrical. [Petteri] designed the PCB to act as the cover for a standard Hammond project box, so all the traces and SMD components are mounted on the back. That just leaves the forest of banana-plug binding posts on the front, along with a couple of pushbuttons for manual input switching and nicely silkscreened labels. The multiplexer is controlled over USB using the SCPI protocol, which happily includes an instrument class for signal switchers.

We think the fit and finish on this one is fantastic, as is usual with one of [Petteri]’s builds. You’ll probably recall his calibrated current reference or his snazzy differential probe.